The long term objective of the proposed work is to further develop and exploit the potential of field-flow fractionation (FFF) as a tool of wide applicability in the biological sciences. The specific development work aimed at this goal will consist mainly of basic theoretical and experimental studies of FFF performance and optimization, the launching of a program to exploit the multidimensional capabilities of FFF, and more limited projects in applications and basic theory. Work will be undertaken to improve performance through the optimization of channel geometry and dimensions, the further development of split inlet and outlet systems, the optimization of hydrodynamic relaxation, and the fuller utilization of digital methods for data interpretation and instrument control. Programmed FFF will be further optimized. A multidimensional FFF system will be developed by linking together sedimentation FFF and flow FFF systems with the objective of more fully characterizing complex colloids such as those of biological origin. Some applications will be undertaken and further work will be done on broader theoretical and methodological issues in analytical separations.